The present invention relates to an AC interconnection solar power generation apparatus and control method therefor.
An example of the use form of a solar power generation system is a DC interconnection system disclosed in Japanese Patent Laid-Open No. 5-108176. In this system, the output from an AC/DC converter 100 that receives commercial power 2 and the output from a solar cell 3 are connected, and the DC power thus obtained is converted into AC power by an inverter 110 and supplied to a load 4, as shown in FIG. 9. Such a system form can be regarded as a simple xe2x80x9cloadxe2x80x9d from the viewpoint of preventing any reverse power flow to the commercial power system. For this reason, when deregulation about electric power greatly progresses in the future, individuals can freely use such a solar power generation system.
In the prior art, however, the capacity of the load 4 is limited by the capacity of the inverter 110. In addition, no measures are taken against unnecessary current leakage of the solar cell 3 due to the stray capacitance to ground, i.e., no device for safety use of the solar cell 3 is disclosed.
Another example that may make it possible to freely use a system as a xe2x80x9cloadxe2x80x9d is an AC interconnection system which prevents any reverse power flow. Unlike the above-described system, commercial power and AC power from a power generator are connected without any conversion and supplied to a load, and the power generator is stopped upon detecting reverse power flow from the power generator to the commercial power system, using a protective relay for detecting reverse power to the commercial power. In this prior art, the limitation on the load capacity due to the output inverter 110 is not present, unlike the arrangement shown in FIG. 9, though the commercial power and power generator parallelly supply power to the load. For this reason, along with an increase in power generated by the power generator, a usable load capacity may exceed the rated load capacity to cause a load current beyond the rated value to flow, resulting in danger.
The present invention has been made to solve these problems, and has as its object to provide an AC interconnection apparatus capable of easily, safely, and efficiently using a solar cell and a control method therefor.
It is another object of the present invention to provide an AC interconnection apparatus capable of preventing any reverse power flow to a commercial power system even when power generated by a solar cell increases in an apparatus which supplies both commercial power and AC power from the solar cell to a load, and a control method therefor.
It is still another object of the present invention to provide an AC interconnection apparatus capable of preventing any overpower to a load in an apparatus which supplies both commercial power and AC power from a solar cell to the load, and a control method therefor.
In order to achieve the above described objects, an AC interconnection apparatus of the present invention comprising the structures as follows.
An AC interconnection apparatus for supplying to a load both AC power from a commercial power system and an output from a solar cell, comprising: an inverter for converting the output from the solar cell into AC power; a current detector arranged between the load and an AC connection point for connecting the AC input from the commercial power system and the AC output from the inverter to detect a current flowing to the load; and control means for obtaining load power applied to the load on the basis of a voltage value at the AC connection point and the current value detected by the current detector and controlling the output of the inverter on the basis of the load power and the output power of said inverter.
In order to achieve the above described objects, a control method for an AC interconnection apparatus of the present invention comprising the steps as follows.
A control method for an AC interconnection apparatus for supplying to a load both AC power from a commercial power system and an output from a solar cell, comprising: a current detection step of detecting a current flowing to the load between the load and an AC connection point for connecting the AC input from the commercial power system and an AC output from an inverter for converting the output from the solar cell into AC power; and a control step of obtaining load power applied to the load on the basis of a voltage value at the AC connection point and the current value detected in the current detection step and controlling the output of the inverter on the basis of the load power and the output power of the inverter.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.